1. Field of the Invention
The present invention relates to an optical pickup actuator and an optical recording and/or reproducing apparatus using the optical pickup actuator, and more particularly, to a tilting movement optical pickup actuator which can be manufactured at a low cost by having a reduced number of magnets, and an optical recording and/or reproducing apparatus using the tilting movement optical pickup actuator.
2. Description of the Related Art
In general, optical pickups are installed in optical recording and/or reproducing apparatuses to record information on and/or reproduce information from a recording medium, such as an optical disc, and move in a radial direction of the optical disc without contacting the optical disc.
Such optical pickups require an actuator, which moves an objective lens in a tracking direction, a focusing direction, and/or a tilting direction to form a laser beam emitted from a light source on a correct portion of the optical disc. A tracking direction movement adjusts the objective lens in a radial direction of the optical disc to form the light spot in the center of a track.
Such an optical pickup actuator carries out tracking and focusing movements, i.e., biaxial movements. In recent years, to facilitate the use of high recording density media, a numerical aperture (NA) of the objective lens has been increased and a wavelength of the light source has been shortened, and consequently a tilting margin of the optical pickup actuator has been decreased. To use high recording density media, the optical pickup actuator requires triaxial movements. A tilting movement, particularly, a radial tilting movement, is required in addition to the existing biaxial movements. Thus, a triaxial movement optical pickup actuator, which is able to perform a tilting movement as well as the existing biaxial movements, is required. The triaxial movement optical pickup actuator is referred to as a tilting movement optical pickup actuator.
The tilting movement optical pickup actuator generally has a structure incorporating a four-sided magnetic circuit. The four-sided magnetic circuit has driving coils and magnets disposed on four sides of a bobbin.
FIG. 1 is a schematic view of an example of a conventional tilting movement optical pickup actuator. Referring to FIG. 1, the conventional tilting movement optical pickup actuator includes a bobbin 2 in which an objective lens is mounted, and a plurality of wires 6a, 6b. One end of each of the wires is fixed on a side of the bobbin 2 and the other end is coupled to a holder 3 disposed on a portion of a base (not shown). This allows the bobbin 2 and a movable portion (not shown) to move with respect to the base in a focusing direction and a tracking direction. A four-sided magnetic circuit moves the moving unit.
Four of the wires 6a serve as suspensions to support the movable portion with respect to the base. Only two of the four suspension wires 6a are shown in FIG. 1. Reference numeral 6b denotes wires used as paths through which a current is applied for a tilting movement.
The four-sided magnetic circuit includes a pair of focusing coils 4a and 4b, positioned on opposite ends of the bobbin 2 in a radial direction of an optical disc, and a pair of tracking coils 4c and 4d installed on opposite sides of the bobbin 2 in a tangential direction of the optical disc. Magnets 5a through 5d interact with currents flowing through the focusing coils 4a and 4b and the tracking coils 4c and 4d to produce electromagnetic forces to drive the movable unit. Yokes 8 are also included.
In the conventional tilting movement optical pickup actuator, upon application of a current to the focusing coils 4a and 4b and the tracking coils 4c and 4d, the current flowing through the focusing coils 4a and 4b and the tracking coils 4c and 4d interacts with a magnetic flux from the magnets 5a through 5d to generate an electromagnetic force that acts in the focusing coils 4a and 4b and the tracking coils 4c and 4d. Thus, the movable portion moves in the focusing direction and the tracking direction. As a result, an objective lens 1 mounted in the bobbin 2 moves in the focusing direction and the tracking direction.
When currents are applied to the respective focusing coils 4a and 4b in opposite directions, electromagnetic forces act in the focusing coils 4a and 4b in opposite directions, and the moving unit moves in a radial tilting direction. As a result, the objective lens 1 mounted in the bobbin 2 moves in the radial tilting direction.
Since the electromagnetic forces act in directions that are parallel to a central axis of the objective lens 1, the magnets 5a and 5b and the focusing coils 4a and 4b are used for focusing and tilting movements. In other words, when currents of equal magnitude and direction are applied to the focusing coils 4a and 4b, a focusing movement with a predetermined displacement is performed. When currents equal in magnitude but opposite in direction are applied to the focusing coils 4a and 4b, a tilting movement is performed.
However, the conventional tilting-movement optical pickup actuator includes a four-sided magnetic circuit having four pre-wound coils 4a through 4d installed on four sides of the bobbin 2, and four magnets 5a through 5d. Thus, the conventional, required use of four coils 4a through 4d and four magnets 5a through 5d increases the number of components and production costs, and results in poor productivity.
The use of pre-wound coils, requires a process of winding the coils and a process of attaching the wound coils to a bobbin. Thus, the number of manufacturing operations is increased. In addition, pre-wound coils are lower in quality than directly wound coils. Further, four magnets are required.
In addition, in the conventional tilting movement optical pickup actuator, magnets face four sides of the bobbin 2, and focusing and tracking coils are positioned on each of the four sides of the bobbin 2 to face the magnets. As a result, wiring between the focusing and tracking coils is complicated.